Project Summary IL-1? is a major player in host defense against invading pathogens. Conversely, excessive IL-1? production and/or activation can be detrimental to the system, resulting in unwanted and exaggerated tissue inflammation. Hence, the bioactivity of IL-1? needs to be well controlled. Mechanisms of IL-1? regulation have traditionally focused on pattern recognition receptor-induced gene transcription and inflammasome-mediated cleavage of pro-IL-1?. The complete IL-1? cytokine regulatory repertoire is still largely unknown. The objective of the proposed research is to identify and characterize biochemical events that modulate the bioactivity of mature IL- 1? after its release from the cells. We recently found that cysteine S-glutathionylation of the highly conserved Cys-188 residue in IL-1? positively regulates IL-1? bioactivity by preventing its irreversible reactive oxygen species (ROS)-elicited oxidation and deactivation. Protein glutathionylation is dynamic and reversible. We further demonstrated that Glutaredoxin 1 (Grx1), an enzyme that catalyzes deglutathionylation, is present and active in the extracellular space in serum and BM, and physiologically regulates IL-1? glutathionylation. Together, these results lead us to hypothesize that ROS-induced cysteine S-glutathionylation and its modulation by Grx1 are key regulatory mechanisms controlling IL-1? activity under pathophysiological conditions. In current study, we will test this hypothesis in a clinically relevant model in which IL-1? activity is both essential and sufficient for efficient recovery of the hematopoietic system after irradiation. First, we will determine the role of cysteine S-glutathionylation in regulating the bioactivity of endogenously produced IL-1? during bone marrow (BM) recovery after irradiation (Aim I). In addition, we will elucidate the function of Grx1 in regulating S-glutathionylation of endogenously produced IL-1? in BM recovery in irradiated mice. We will also identify the cell types that produce Grx1 in the BM (Aim II). Finally, we will try to accelerate BM recovery after irradiation by targeting IL-1? S-glutathionylation. We will first examine whether glutathione intravenous injection (GSH IV) therapy can elevate IL-1? bioactivity and accelerate the recovery of the hematopoietic system in irradiated mice. In addition, we will investigate whether IL-1? 188C/S, a mutant form of IL-1? that can not be oxidized and deactivated, is more potent in eliciting BM protective effect in irradiated mice compared to WT IL- 1? (Aim III). Together, experiments proposed in these three specific aims will provide a better understanding of the role of ROS-induced cysteine S-glutathionylation in controlling IL-1? activity in vivo in clinically relevant settings. Toward the translational research paradigm, results from this study will assist us to identify novel therapeutic targets (e.g. ROS, Grx1, and related pathways) for accelerating BM recovery in patients receiving radiotherapy.